Manoj Joshi

Chlorophyll regulates solar radiation absorption in the upper ocean, influencing the ocean's mean state and climate. However, its response to climate change in Earth System Models (ESMs) remains unclear. Here, we show that in addition to well‐known effects on the carbon cycle, projected chlorophyll decline reduces the absorption of solar radiation within the ocean's mixed layer, effectively redistributing 0.1–0.87 W m ⁻² of globally‐averaged radiative flux to the upper thermocline underneath it. Based on an idealized assessment of the heat‐equivalent effect, this redistribution may delay surface warming by 2–12 years under the SSP5‐8.5 scenario. The uncertainty arises from inter‐model differences in the simulation of chlorophyll and its solar absorption in ESMs that simulate these processes. Such differences also contribute to biases in the mean pre‐industrial state of ESMs. Our findings highlight the need to reduce uncertainty in physical, not just biogeochemical, feedbacks associated with chlorophyll in ESMs.

Asian sulfate aerosols substantially affect regional summer precipitation, yet whether and how their effects vary with the background climate state remains unclear. This study investigates these impacts under pre-industrial and pre-industrial +1 K climates, using the reduced-complexity climate model Fast Ocean Rapid Troposphere Experiment version 2 with the Systematic Regional Aerosol Perturbations simulations. Results show that increased Asian sulfate aerosols reduce the summer mean and extreme precipitation over East and South Asia in both climates, with stronger suppression over northern India in the +1 K climate. The atmospheric energy budget analysis reveals that this is primarily due to enhanced dynamic effects in the warmer climate. When aerosols are added to the pre-industrial climate, the increased horizontal dry static energy (DSE) gradient partially offsets the aerosol-induced dynamic suppression over northern India. Under the +1 K climate, higher atmospheric static stability weakens the local meridional circulation induced by aerosol forcing, thereby reducing the meridional temperature gradient and diminishing the offsetting effect, making the dynamic suppression more dominant. Further analysis indicates that this difference in precipitation responses results from the nonlinear interaction between the aerosol-radiation and aerosol-cloud interactions under the +1 K climate, whereas the two effects combine approximately linearly under the pre-industrial climate. This study suggests that the reduction in precipitation, including extremes, over northern India caused by Asian sulfate aerosols is amplified under a warmer climate background. This implies that future aerosol emissions reductions may unmask or amplify extreme precipitation increases in this region.

The South Pacific Convergence Zone (SPCZ) is the dominant perennial rainfall feature of the Southern Hemisphere, yet the physical mechanisms driving its variability on decadal to multidecadal time‐scales are poorly understood. Using prescribed sea‐surface temperature (SST) perturbations in the atmosphere‐only Intermediate Global Circulation Model version 4 (IGCM4), we investigate the direct atmospheric mechanisms by which three major modes of low‐frequency climate variability—the Interdecadal Pacific Oscillation (IPO), Atlantic Multidecadal Variability (AMV), and Southern Ocean SST‐driven midlatitude jet shifts—modulate the South Pacific hydroclimate. IPO forcing produces the most substantial and spatially coherent SPCZ response: a positive IPO anomaly drives a northeastward shift in the SPCZ, while a negative IPO shifts the SPCZ southwestward. This behaviour arises from coupled dynamic and thermodynamic changes, with anomalous moisture convergence—rather than altered Rossby‐wave refraction—emerging as the dominant control on SPCZ position. By contrast, AMV‐forced atmospheric teleconnections exert only weak and statistically insignificant impacts on South Pacific precipitation; any apparent signal is best interpreted as an alias of IPO‐like SST anomalies in the Pacific. Southern Ocean SST anomalies induce significant shifts in the Southern Hemisphere midlatitude jet and associated Hadley–Ferrel cell structure, but these changes do not generate a coherent SPCZ displacement. Instead, precipitation changes reflect large‐scale regions of anomalous ascent and descent, driven by Hadley and Ferrel cell shifts, rather than modifications to SPCZ dynamics.

FORTE 3 is an intermediate-resolution coupled atmosphere–ocean general circulation model (AOGCM) consisting of the Intermediate General Circulation Model 4 (IGCM4.1), a T42 spectral atmosphere with 35 σ-layers, coupled to Modular Ocean Model – Array (MOMA), a 2° × 2° ocean with 15 z-layer depth levels. It is a significant upgrade from its predecessor, the fast flexible AOGCM FORTE2, in terms of its mean climate and climate response. The model has been compiled using the Intel ifx compiler. Here we describe the changes between FORTE2 and FORTE3 and demonstrate its use by simulating global and Pacific ocean change under both idealised CO2 forcing and stratospheric O3 depletion. In the atmosphere a new formulation for convective entrainment in IGCM4.1 alleviates a cold upper tropospheric bias in IGCM4. The formulation for precipitating convection has been changed to reduce an existing strong negative cloud forcing bias in the model, and a new formulation for stratocumulus cloud has been introduced. Effects of changes are especially evidenced in climate simulations: the transient climate response in FORTE3 is 1.8 K, and the equilibrium climate sensitivity in a slab version of IGCM4.1 is 4.2 K, compared to FORTE2/slab IGCM4 values of 1.0 K and 2.1 K respectively, and are more consistent with CMIP6 GCMs and observations. In the ocean, a new parameterisation of equatorial mixing based on the meridional sea surface temperature gradient alleviates the equatorial cold bias. The Atlantic Meridional Overturning Circulation at 30° N is 17 Sv, while the transport of the Antarctic Circumpolar Current is 130 Sv, slightly stronger, and more in agreement in observations than FORTE2. We demonstrate the use of FORTE3 by conducting sensitivity experiments where CO2 is increased by 1 % per year. We find that the introduction of a "high-volume" Andes mountain range does not change the pattern of global warming over the Pacific Ocean; conversely, the effect of stratospheric O3 depletion does appear to change the equatorial Pacific gradient slightly.

This study investigates the impact of Asian sulfate aerosols on regional summer extreme precipitation under both pre-industrial and pre-industrial +1 K climate states, using the reduced-complexity climate model Fast Ocean Rapid Troposphere Experiment version 2 (FORTE2) with Systematic Regional Aerosol Perturbations simulations. Results show that increased Asian sulfate aerosols reduce extreme precipitation, characterized by lower frequency and weaker intensity over East and South Asia in both climates, but the suppression is more pronounced over northern India in the +1 K climate. Atmospheric energy budget analysis reveals this is primarily due to enhanced dynamic effects in the warmer climate. When aerosols are added to the pre-industrial climate state, an increased horizontal dry static energy (DSE) gradient partially offsets the aerosol-induced dynamic suppression over northern India. Under the +1 K climate, higher atmospheric static stability weakens the local meridional circulation induced by aerosol forcing, reducing the meridional temperature gradient and thus diminishing the offsetting effect, making the dynamic suppression more dominant. Further analysis indicates that this difference in precipitation responses between the two climates results from the nonlinear effect between the aerosol-radiation and aerosol-cloud interactions under the +1 K climate, whereas the two effects combine approximately linearly under the pre-industrial climate. This study suggests that continued global warming alone will exacerbate Asian sulfate aerosols’ weakening of precipitation, including extremes, over northern India. This implies that future reductions in aerosol emissions may unmask or amplify extreme precipitation increases in this region.

This study investigates the impact of Asian sulfate aerosols on regional summer extreme precipitation under both pre-industrial and pre-industrial +1 K climate states, using the reduced-complexity climate model Fast Ocean Rapid Troposphere Experiment version 2 (FORTE2) with Systematic Regional Aerosol Perturbations simulations. Results show that increased Asian sulfate aerosols reduce extreme precipitation, characterized by lower frequency and weaker intensity over East and South Asia in both climates, but the suppression is more pronounced over northern India in the +1 K climate. Atmospheric energy budget analysis reveals this is primarily due to enhanced dynamic effects in the warmer climate. When aerosols are added to the pre-industrial climate state, an increased horizontal dry static energy (DSE) gradient partially offsets the aerosol-induced dynamic suppression over northern India. Under the +1 K climate, higher atmospheric static stability weakens the local meridional circulation induced by aerosol forcing, reducing the meridional temperature gradient and thus diminishing the offsetting effect, making the dynamic suppression more dominant. Further analysis indicates that this difference in precipitation responses between the two climates results from the nonlinear effect between the aerosol-radiation and aerosol-cloud interactions under the +1 K climate, whereas the two effects combine approximately linearly under the pre-industrial climate. This study suggests that continued global warming alone will exacerbate Asian sulfate aerosols’ weakening of precipitation, including extremes, over northern India. This implies that future reductions in aerosol emissions may unmask or amplify extreme precipitation increases in this region.

This study investigates the impact of Asian sulfate aerosols on regional summer extreme precipitation under both pre-industrial and pre-industrial +1 K climate states, using the reduced-complexity climate model Fast Ocean Rapid Troposphere Experiment version 2 (FORTE2) with Systematic Regional Aerosol Perturbations simulations. Results show that increased Asian sulfate aerosols reduce extreme precipitation, characterized by lower frequency and weaker intensity over East and South Asia in both climates, but the suppression is more pronounced over northern India in the +1 K climate. Atmospheric energy budget analysis reveals this is primarily due to enhanced dynamic effects in the warmer climate. When aerosols are added to the pre-industrial climate state, an increased horizontal dry static energy (DSE) gradient partially offsets the aerosol-induced dynamic suppression over northern India. Under the +1 K climate, higher atmospheric static stability weakens the local meridional circulation induced by aerosol forcing, reducing the meridional temperature gradient and thus diminishing the offsetting effect, making the dynamic suppression more dominant. Further analysis indicates that this difference in precipitation responses between the two climates results from the nonlinear effect between the aerosol-radiation and aerosol-cloud interactions under the +1 K climate, whereas the two effects combine approximately linearly under the pre-industrial climate. This study suggests that continued global warming alone will exacerbate Asian sulfate aerosols’ weakening of precipitation, including extremes, over northern India. This implies that future reductions in aerosol emissions may unmask or amplify extreme precipitation increases in this region.

This study investigates the impact of Asian sulfate aerosols on regional summer extreme precipitation under both pre-industrial and pre-industrial +1 K climate states, using the reduced-complexity climate model Fast Ocean Rapid Troposphere Experiment version 2 (FORTE2) with Systematic Regional Aerosol Perturbations simulations. Results show that increased Asian sulfate aerosols reduce extreme precipitation, characterized by lower frequency and weaker intensity over East and South Asia in both climates, but the suppression is more pronounced over northern India in the +1 K climate. Atmospheric energy budget analysis reveals this is primarily due to enhanced dynamic effects in the warmer climate. When aerosols are added to the pre-industrial climate state, an increased horizontal dry static energy (DSE) gradient partially offsets the aerosol-induced dynamic suppression over northern India. Under the +1 K climate, higher atmospheric static stability weakens the local meridional circulation induced by aerosol forcing, reducing the meridional temperature gradient and thus diminishing the offsetting effect, making the dynamic suppression more dominant. Further analysis indicates that this difference in precipitation responses between the two climates results from the nonlinear effect between the aerosol-radiation and aerosol-cloud interactions under the +1 K climate, whereas the two effects combine approximately linearly under the pre-industrial climate. This study suggests that continued global warming alone will exacerbate Asian sulfate aerosols’ weakening of precipitation, including extremes, over northern India. This implies that future reductions in aerosol emissions may unmask or amplify extreme precipitation increases in this region.

M dwarfs are the most promising candidates for finding habitable worlds through atmospheric characterization. Planets in the habitable zone of low-mass stars experience intense tidal forcings and often become tidally locked. Despite the majority of research being centered on the climate dynamics of synchronously rotating planets in this scenario, synchronous rotation is not an inevitable outcome of tidal locking. Several different circumstances can result in an asynchronous rotation and, in some instances, can lead to spin–orbit resonances (SORs). We explore the climates of two different SOR scenarios with a coupled atmosphere–ocean general circulation climate model. Given the crucial role played by the oceans in shaping planetary climate, we adopt two different ocean tidal forcing parameterizations for each SOR scenario. Each of these cases is simulated with both a dynamic ocean and a thermodynamic ocean. Our findings reveal striking differences between the analyzed resonant case and the commonly studied synchronous rotation case. Periodic climate patterns are observed, with climatic features such as clouds and rainfall exhibiting a 60 ^∘ longitudinal shift relative to the substellar point. The evolution of quantities such as thermal emission and reflected light during a stellar period is noteworthy from the observational point of view, showing appreciable differences compared to the synchronous rotation scenario.

This study investigates the impact of Asian sulfate aerosols on regional summer extreme precipitation under both pre-industrial and pre-industrial +1 K climate states, using the reduced-complexity climate model Fast Ocean Rapid Troposphere Experiment version 2 (FORTE2) with Systematic Regional Aerosol Perturbations simulations. Results show that increased Asian sulfate aerosols reduce extreme precipitation, characterized by lower frequency and weaker intensity over East and South Asia in both climates, but the suppression is more pronounced over northern India in the +1 K climate. Atmospheric energy budget analysis reveals this is primarily due to enhanced dynamic effects in the warmer climate. When aerosols are added to the pre-industrial climate state, an increased horizontal dry static energy (DSE) gradient partially offsets the aerosol-induced dynamic suppression over northern India. Under the +1 K climate, higher atmospheric static stability weakens the local meridional circulation induced by aerosol forcing, reducing the meridional temperature gradient and thus diminishing the offsetting effect, making the dynamic suppression more dominant. Further analysis indicates that this difference in precipitation responses between the two climates results from the nonlinear effect between the aerosol-radiation and aerosol-cloud interactions under the +1 K climate, whereas the two effects combine approximately linearly under the pre-industrial climate. This study suggests that continued global warming alone will exacerbate Asian sulfate aerosols’ weakening of precipitation, including extremes, over northern India. This implies that future reductions in aerosol emissions may unmask or amplify extreme precipitation increases in this region.